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Hearing Protection (Ear Defenders): Rigid Cups on Liquid-Filled Cushions (Shaw & Thiessen, NRC, US 2,801,423, 1957)
Ear muffs that seal well and still stop low-pitched noise. Each ear is covered by a rigid cup on a cushion made of a thin PVC tube, emptied of air and part-filled with liquid. Pressed on, the liquid flows round the whole rim and fits the cushion to the head, yet cannot compress, so the cup does not vibrate as a whole and pass the sound in. A sprung headband with a pad holds the cups on ball joints.
Result: circumaural ear defenders effective against low-frequency noise.
Source: E. A. G. Shaw and G. J. Thiessen (National Research Council of Canada), US 2,801,423 (1957). Unknown: sizes and the attenuation achieved. Picture: the patent drawing.
Kati
Unknown
Maagizo
1
1
Make the cups
Make the cups
Make two rigid, non-porous cups to go over the ears, of wood, a hard plastic or a light metal such as aluminium. Widen each rim to about the width of the cushion, and make a small hole in the rim for the cushion's filling nipple. Fix a ball joint on the back of each cup. Not given: sizes.
Vifaa kwa hatua hii:
Nyenzo isiyojulikana2 vikombe
Metali isiyojulikana2 ball jointsZana zinazohitajika:
Kereza ya Chuma
Vipimo visivyojulikana2
2
Make the liquid cushions
Make the liquid cushions
For each cup make an endless tube of thin, pliable but non-stretching plasticised PVC, 0.005 to 0.01 in thick, with a filling nipple. Draw out almost all the air, then fill it with liquid to more than a quarter but well under the whole of its cross-section: enough to reach right round the rim when pressed, not so much that it cannot seal. Fix it on the rim with the nipple in the hole. Ours: water as the liquid. Not given: tube size.
Vifaa kwa hatua hii:
Bati la PVC1 thin plasticised PVC tube
Maji1 fillingZana zinazohitajika:
Seti ya sindano za kunyonya3
3
Fit the headband and wear them
Fit the headband and wear them
Make a resilient headband frame with a sponge-rubber pad at its middle and a wire loop at each end. Through each loop pass a threaded stub from the cup's ball joint, with a washer, and tighten with a wing nut. Put the cups over the ears: the cushions take the shape of the head and seal, while the cups stay still against the low-frequency sound. Ours: spring steel for the frame.
Vifaa kwa hatua hii:
Waya wa chuma cha kamani1 frame and loopsNyenzo isiyojulikana1 sponge rubber padMetali isiyojulikana2 threaded stubs
Washa bapa2 vipande
Nati ya mabawa2 vipandeZana zinazohitajika:
Koleo lenye Ncha za DuaraVifaa
7- 1 sponge rubber padKishikilia Nafasi
- 2 threaded stubsKishikilia Nafasi
- 1 thin plasticised PVC tubeKishikilia Nafasi
- 1 fillingKishikilia Nafasi
- 1 frame and loopsKishikilia Nafasi
- 2 vipandeKishikilia Nafasi
- 2 vipandeKishikilia Nafasi
Zana Zinazohitajika
4- Kishikilia Nafasi
- Kishikilia Nafasi
- Kishikilia Nafasi
- Kishikilia Nafasi
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